1. Field of the Invention
The present invention relates to semiconductor processing technology and, more specifically, to using spin-on, photopatternable, interlayer dielectric materials at additional wavelengths of radiation.
2. State of the Art
Photoresist layers are used for making miniaturized electronic components when fabricating semiconductor devices, such as computer chips and integrated circuits. During fabrication, a thin photoresist layer is typically applied to a semiconductor substrate. The photoresist layer is then baked to evaporate solvent in the photoresist and to fix the photoresist onto the semiconductor substrate. To form a pattern on the photoresist layer, portions of the layer are exposed to radiation, such as visible light, ultraviolet (“UV”) light, electron beam (“EB”), or X-ray radiant energy, through a mask. The radiation causes a photochemical reaction in portions of the photoresist layer that are exposed to the radiation, which changes the solubility of these portions. The solubility of unexposed portions of the photoresist layer is unchanged. The semiconductor substrate is treated with a developer solution that is selected to solubilize and remove the radiation-exposed portions of the photoresist layer. Since the exposed portions of the photoresist layer are removed, a desired pattern is formed in the photoresist layer. The pattern is transferred to underlying layers of the semiconductor device by conventional techniques, such as by wet or dry etching processes. The remaining portions of the photoresist layer are removed once the pattern is transferred to the underlying layers of the semiconductor device.
As memory requirements for the semiconductor devices have increased, the size of the electronic components in the semiconductor devices has decreased. To accomplish the decreased size, new photoresist materials sensitive to short wavelengths of radiation have been developed because the short wavelengths provide better resolution of features on the semiconductor devices. As used herein, the term “short wavelength” refers to a wavelength of approximately 100 nm to approximately 300 nm. Photoresist materials sensitive to this wavelength range are typically used when subhalfmicron geometries are required. For instance, photoresist materials sensitive to 248 nm are currently being used while photoresist materials sensitive to 193 nm are under development.
Spin-on, photopatternable, interlayer dielectric (“ILD”) materials are known in the art and are available from sources, such as Clariant International, Ltd. (Muttenz, Switzerland). These ILD materials are photoresist materials that are convertible to a silica-type ceramic film when exposed to radiation. As disclosed in EP 1239332 to Nagahara et al., a photoresist composition that includes a polysilazane (“PSZ”) compound and a photoacid generator (“PAG”) is applied to a semiconductor wafer to form a photoresist layer. The photoresist layer is exposed to UV radiation, such as radiation of 360-430 nm, or EB radiation through a mask. In the exposed, or unmasked, portions of the photoresist layer, the radiation initiates the photochemical reaction and produces protons from the PAG. The protons are generated from an acid, which is produced by the photochemical reaction. No reaction occurs in the unexposed, or masked, portions of the photoresist layer and, therefore, no protons are produced in these portions of the photoresist layer. The protons react with oxygen (“O2”) and/or water (“H2O”) in the atmosphere to cleave Si—N bonds that are present in the PSZ. Subsequently, H2O reacts with the cleaved PSZ to form a methyl silsesquioxane (“MSQ”), which contains Si—O bonds. Since the protons are only formed in the exposed portions of the photoresist layer, selected portions of the photoresist layer are converted to the silica-type ceramic film. The silica-type ceramic film is selectively removed using tetramethylammonium hydroxide (“TMAH”), leaving the unexposed portions of the photoresist layer to create the desired pattern on the semiconductor substrate. These remaining portions are subsequently exposed to radiation of 360-430 nm to convert the photoresist layer into the silica-type ceramic film. The silica-type ceramic film has a low dielectric constant, has good insulating properties, is resistant to heat, abrasion, and corrosion, and is used in semiconductor devices, liquid crystal displays, and printed circuit substrates to form ILDs.
Additional photoresist materials that are convertible to an insulative material by exposure to radiation are disclosed in U.S. Pat. No. 6,350,706 to Howard. A plasma polymerized methylsilane is selectively converted to photo-oxidized siloxane, an insulative material, by exposure to deep ultraviolet (“DUV”) radiation. Semiconductor device structures are formed by converting exposed portions of the photoresist material to the insulative material. By converting the photoresist material into the insulative material, a permanent structure is formed and the photoresist material does not have to be removed by an etch process.
One disadvantage of these photoresist materials is that they are sensitive to a single wavelength or narrow range of wavelengths. In other words, the conversion of the PSZ to the silica-type ceramic film occurs most efficiently at that wavelength(s), which typically ranges from 360 to 430 nm. At these wavelengths, a high degree of resolution is not possible, such as the resolution achieved by the 193 nm or 243 nm photoresists currently being developed and used. However, these latter wavelengths (193 nm or 243 nm) do not efficiently convert the PSZ to the silica-type ceramic film. Therefore, the application of these photoresist or ILD materials for front-end applications, where a short wavelength is essential to achieve the desired resolution, is severely limited. In addition, it is not possible to optimize both the patterning process and the conversion process and, as such, a user must compromise, or choose between, achieving each of these processes.
It would be desirable to be able to use the ILD materials at additional wavelengths, especially short wavelengths, so that the ILD materials are useful in a broader range of applications. It would also be desirable to be able to perform both the patterning process and the conversion process at conditions optimal for each process without having to compromise between achieving optimal patterning and optimal conversion.